Monolithic LED chip in an integrated control module with active circuitry

ABSTRACT

A lighting device includes a monolithic LED chip flip-chip mounted onto an interconnect structure. The monolithic chip includes LED junctions formed from a single LED junction. An active electronic component is also mounted onto the interconnect structure at a distance from the monolithic chip that is less than five times the maximum dimension of the monolithic chip. The active electronic component controls LED drive currents independently supplied to the LED junctions. Different types of phosphor are disposed laterally above the various LED junctions. A color sensor measures the light emitted from the lighting device when drive currents are supplied to first and second LED junctions. The active electronic component then supplies more drive current to the first LED junction than to the second LED junction in response to the color sensor measuring the light emitted when the prior LED drive currents are supplied to the first and second LED junctions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims; priority under 35U.S.C. §120 from, nonprovisional U.S. patent application Ser. No.14/318,383 entitled “Monolithic LED Chip in an Integrated Control Modulewith Active Circuitry,” now U.S. Pat. No. 9,277,618, filed on Jun. 27,2014, the subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to packaging of light-emittingdiodes.

BACKGROUND INFORMATION

A light emitting diode (LED) is a solid state device that convertselectrical energy to light. Light is emitted from active layers ofsemiconductor material sandwiched between oppositely doped layers when avoltage is applied across the doped layers. In order to use an LED chip,the chip is typically enclosed along with other LED chips in a package.In one example, the packaged device is referred to as an LED array. TheLED array includes an array of LED chips mounted onto a heat conductingsubstrate. A layer of silicone in which phosphor particles are embeddedis typically disposed over the LED chips. Electrical contact pads areprovided for supplying current into the LED array and through the LEDchips so that the LED chips can be made to emit light. Light emittedfrom the LED chips is absorbed by the phosphor particles, and isre-emitted by the phosphor particles so that the re-emitted light has awider band of wavelengths. Making a light fixture or a “luminaire” outof such an LED array, however, typically involves other components. TheLED array generates heat when used. If the temperature of the LED arrayis allowed to increase excessively, performance of the LED array maysuffer and the LED array may actually fail. In order to remove enoughheat from the LED array so as to keep the LED array adequately cool, theLED array is typically fixed in some way to a heat sink. In addition,power must be supplied to the LED array. Power supply circuitry istypically required to supply current to the LED array in a desired andsuitable fashion. Optical components are also generally employed todirect and focus the emitted light in a desired fashion. There are manyconsiderations involved in packaging an LED array so that the array canbe used effectively in an overall luminaire. Improved ways of packagingLED arrays for use in luminaires are sought.

SUMMARY

A lighting device includes a monolithic LED chip flip-chip mounted ontoan interconnect structure. The monolithic chip includes first and secondLED PN junctions that are formed from a single LED junction. An activeelectronic component is also mounted onto the interconnect structure inthe proximity of the monolithic chip at a distance from the chip that isless than five times the maximum dimension of the chip. A molded plasticencapsulant forms the upper surface of the lighting device and contactsand covers the active electronic component. The active electroniccomponent controls the LED drive currents independently supplied to thefirst and second LED junctions. None of the LED junctions of themonolithic LED chip is coupled to any other LED junction using wirebonds.

A first type of phosphor particles is disposed laterally above the firstLED junction, and a second type of phosphor particles is disposedlaterally above the second LED junction. The phosphor particles aresuspended in a layer of silicone that covers the monolithic chip. Acolor sensor also mounted onto the interconnect structure measures thelight emitted from the lighting device when the LED drive currents aresupplied to the first and second LED junctions. The active electroniccomponent then supplies more LED drive current to the first LED junctionthan to the second LED junction in response to the color sensormeasuring the light emitted when the prior LED drive currents aresupplied to the first and second LED junctions. The light emitted fromthe lighting device has a first color temperature when the prior LEDdrive currents are supplied to the first and second LED junctions and asecond color temperature when the LED drive current supplied to thefirst LED junction is increased.

Metallic vias pass through the interconnect structure from its uppersurface to its lower surface. The metallic vias are disposed laterallybeneath the monolithic LED chip. No electric current flows through themetallic vias. The vias are filled with solid metal and conduct heatgenerated by the monolithic LED chip to a heat sink attached to thelower surface of the interconnect structure. A thermal insulator isdeposited as a layer over the lower surface of the interconnectstructure laterally outside the footprint of the monolithic LED chip.The thermal insulator impedes heat that is generated by the LEDjunctions and that flows through the metallic vias and into the heatsink from flowing back up through the lower surface of the interconnectstructure and into the active electronic components.

A method involves emitting light from one of the LED junctions of themonolithic LED chip while determining the temperature of the chip usinganother of the LED junctions. Each of the LED junctions has a galliumnitride (GaN) layer and exhibits a band gap that exceeds two electronvolts. Both of the LED junctions are formed from a single LED junction.The first LED junction is illuminated by supplying an LED drive currentto the first LED junction. The temperature of the second LED junction isdetermined by determining a voltage across the second LED junction. Theactive electronic component supplies the second LED junction with aconstant current and concurrently determines the voltage across thesecond LED junction. The active electronic component determines thetemperature of the second LED junction based on the voltage across thesecond LED junction.

Further details and embodiments and techniques are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 is a perspective view of an integrated control module (ICM) witha monolithic LED chip.

FIG. 2 is a more detailed view of the monolithic LED chip of FIG. 1.

FIG. 3 is a cross sectional view illustrating the general structure ofthe layers of the monolithic LED chip of FIG. 1.

FIG. 4 is a top perspective view of the ICM of FIG. 1 from the oppositeside.

FIG. 5 is an expanded perspective view of the monolithic LED chip, aredistribution layer of the LED chip and the upper surface of aninterconnect structure upon which the LED chip is to be flip-chipmounted.

FIG. 6 is a perspective view of the bottom of the ICM of FIG. 1.

FIG. 7 is a cross-sectional view of the bottom of the ICM of FIG. 1.

FIG. 8 is a cross-sectional view taken along line A-A′ of the ICM ofFIG. 1 showing the ICM being attached to a heat sink by bolts.

FIG. 9 is a cross-sectional view taken along line B-B′ of the ICM ofFIG. 1 showing a color sensor embedded in the slanted upper surface ofthe molded encapsulant of the ICM of FIG. 1.

FIG. 10 is a cross-sectional view taken along line C-C′ of the ICM ofFIG. 1 showing electronic components mounted onto the interconnectstructure within a distance from the LED chip that is less than fivetimes the maximum dimension of the LED chip.

FIG. 11 is a circuit diagram showing a first implementation of thecontrol circuitry of the ICM of FIG. 1.

FIG. 12 is a diagram of a lighting system that includes the ICM of FIG.11.

FIG. 13 is a circuit diagram showing a second implementation of thecontrol circuitry of the ICM of FIG. 1 that includes a buck converter.

FIG. 14 is a diagram illustrating a first way to drive multiple stringsof LED junctions with multiple buck converters, where the multiple buckconverters are parts of the ICM of FIG. 13.

FIG. 15 is a diagram illustrating a second way to drive multiple stringsof LED junctions with multiple buck converters, where the multiple buckconverters are parts of the ICM of FIG. 13.

FIG. 16 is a diagram of a lighting system that includes multipleinstances of the ICM of FIG. 13.

DETAILED DESCRIPTION

Reference will now be made in detail to examples and some embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a top perspective view of an integrated control module (“ICM”)10. ICM 10 is a disk-shaped structure that includes a plasticencapsulant 11 molded over an interconnect structure 12 upon which amonolithic light emitting diode (LED) chip 13 is mounted. The integratedcontrol module 10 allows active electronic components to be embedded inthe plastic encapsulant 11 in close proximity to the LED chip 13. Theactive electronic components monitor, control and provide power to theLED chip 13. Thus, integrated control module 10 is a compact, low-cost,intelligent LED package that can be incorporated into a luminaire usingminimal external components.

ICM 10 has a circular upper outer peripheral edge 15 that circumscribesa toroidal upper surface 16 formed by plastic encapsulant 11. Two holes17 and 18 are provided through which threaded screws or bolts can extendto attach ICM 10 to a heat sink. A portion of the upper surface 14 ofinterconnect structure 12 is visible through a circular central opening19 in ICM 10. In this embodiment, interconnect structure 12 is amulti-layer printed circuit board (PCB). For example, interconnectstructure 12 is an FR-4 printed circuit board with several metal layersmade of woven fiberglass fabric with an epoxy resin binder. In otherembodiments, structures such as Kapton “flex circuit” or metal clad PCBcircuits can also be used for the interconnect structure. When the LEDPN junctions of monolithic LED chip 13 are powered and emitting light,the light passes upward through the central circular opening 19 in uppersurface 16 and is transmitted upward and away from ICM 10.

FIG. 2 shows monolithic LED chip 13 in more detail. Monolithic LED chip13 is flip-chip mounted onto interconnect structure 12. FIG. 2 showschip 13 before it is inverted for flip-chip mounting. Monolithic LEDchip 13 has multiple LED PN junctions all formed from the same singleLED PN junction. Each of the LED junctions includes a portion of thecommon epitaxial layers of GaN or GaInN that were grown on a sapphiresubstrate. In other embodiments, the gallium-nitride layers are grown ona substrate of crystalline silicon.

Monolithic LED chip 13 is made in a similar manner as are LED chips ofconventional LED arrays except that chip 13 is not diced. FIG. 3illustrates the general structure of the layers of monolithic LED chip13. A buffer layer 20 is disposed on a sapphire substrate 21. An n-typegallium nitride (n-GaN) layer 22 is disposed over the buffer layer 20;an active layer 23 is disposed over the n-GaN layer 22; and a p-GaNlayer 24 is disposed over the active layer 23. A top layer 25 of silicondioxide over a mesh of indium tin oxide (ITO) is disposed over p-GaNlayer 24. Other intervening layers of the multi-layer epitaxialstructure are not shown in the simplified illustration of FIG. 3.

Reference numeral 26 identifies a sidewall formed by an N-trench 27. Ametal N-electrode 28 is disposed at the bottom of N-trench 27 at theright of the diagram, whereas a metal P-electrode 29 is disposed at theleft of the diagram on top of the silicon dioxide layer 25. The P-typeelectrode 29 makes electrical contact to the ITO mesh beneath it throughmany small holes that extend through the silicon dioxide of layer 25.The metal of the P-electrode 29 extends down into these holes in thesilicon dioxide and makes contact with the top of the ITO. Similarly,N-type electrode 28 at the right of the diagram makes electrical contactto the underlying n-GaN layer 22 through many holes in the silicondioxide. A passivation layer 30 covers the entire structure of thecross-sectional view of FIG. 3. Although the passivation layer 30 coversthe entire portion of the structure illustrated in the cross-section ofFIG. 3, there are openings in the passivation layer 30 over theelectrodes where contact is made to the chip pad redistribution layer(RDL) 31 above.

Returning to FIG. 2, the LED chip structure of FIG. 3 is built up overthe entire monolithic LED chip 13 of FIG. 2. Monolithic LED chip 13 isshown in FIG. 2 without passivation layer 30 and with the redistributionlayer 31 elevated above the rest of the chip. The single LED PN junctionof the chip is separated into the individual LED PN junctions usingetching, photolithography, deposition or ion implantation. Chip 13 hasbeen separated into sixteen separate LED junctions. All of the LEDjunctions of the monolithic LED chip 13 share at least one commoncrystalline layer. FIG. 2 shows that all of the LED junctions sharesapphire substrate 21 and buffer layer 20. The individual LED junctionsare made by etching down into the p-GaN 24, active 23 and n-GaN 22layers to separate the junctions. An insulator 32 is then deposited intothe channels that separate the individual LED junctions.

Various of the LED junctions are electrically connected into strings ofserially connected LED junctions. The metal N-electrode 28 of one LEDjunction is built up with a conductive pedestal 33 which is electricallycoupled to the metal P-electrode 29 of the next LED junction in thestring. The P-electrode 29 extends across two sides of the top of theLED junction in order to spread the LED drive current better over thep-GaN layer 24 below. The first P-electrode 29 and the last N-electrode28 of each string, such as P-electrode 34 and the last N-electrode 35 inFIG. 2, are then coupled to chip pads 36-37 in the redistribution layer31 above. The sixteen LED junctions of FIG. 2 are arranged in fourstrings of four LED junctions each. Monolithic LED chip 13 is thenflip-chip mounted onto upper surface 14 of interconnect structure 12such that the light emitted from the LED junctions exits through thetransparent sapphire substrate 21.

Returning to FIG. 1, the embodiment of LED chip 13 in FIG. 1 also hassixteen LED junctions arranged in a four-by-four matrix. The sapphiresubstrate 21 is facing up in FIG. 1. One of the strings, however,includes only three LED junctions. FIG. 1 shows a first string of fourserially connected LED junctions 38 and a second string of four seriallyconnected LED junctions 39. An electrical current applied to a first LEDjunction of each string spreads to all the LED junctions of the string.No LED junction of monolithic LED chip 13 is coupled to any other LEDjunction using wire bonds. In addition, no LED junction is electricallyconnected to interconnect structure 12 using wire bonds. A chip pad ateach end of the strings is flip-chip connected to a landing pad on theupper surface of interconnect structure 12.

One of the LED junctions 40 is not serially connected to any other LEDjunction but rather is connected directly to terminals on interconnectstructure 12. LED junction 40 may be connected either to terminalsdirectly beneath it or through landing pads on interconnect structure 12at the periphery of monolithic LED chip 13. The remaining three LEDjunctions in the row with junction 40 are serially connected to oneanother and form a string of three LED junctions. Drive current is notpassed through sensor LED junction 40, and LED junction 40 is notconnected to power supply terminals or other driver circuitry. Instead,LED junction 40 is connected to electronic components that supply LEDjunction 40 with a constant current and that determine the voltageacross LED junction 40. At a constant current flowing through LEDjunction 40, the voltage across LED junction 40 depends on thetemperature of LED junction 40. LED junction 40 is thereby used todetermine the temperature of monolithic LED chip 13. As LED junction 40is structurally identical to the other LED junctions and includes atleast one common crystalline layer, the temperature of LED junction 40is nearly identical to the temperatures of the other LED junctions ofmonolithic LED chip 13. The temperature of all of the LED junctions doesnot vary by more than a couple of degrees.

The voltage across gallium-nitride LED junction 40 while a constantcurrent is flowing varies linearly with its temperature. The voltageacross LED junction 40 decreases as the temperature increases while theconstant current is flowing. For example, the control circuitry candetermine that the temperature of LED junction 40 is about 105° C. ifthe voltage across LED junction 40 is 2.45 volts while a constantcurrent of 5 mA is flowing through LED junction 40. The voltage across adiode through which a constant current is flowing varies withtemperature according to the relationship V=C−T/B, where C is indicativeof the constant current, and B is indicative of the band gap energy ofthe diode. For a constant current of 5 mA, C equals 2.5873. For agallium-nitride LED junction that emits light at 452 nanometers, Bequals 769.231. Thus, the temperature-voltage relationship can beexpressed as V=2.5873−T/769.231. Using the voltage V across sensor LEDjunction 40 as an input, the control circuitry of ICM 10 calculates thetemperature of LED chip 13 using the formula T=769.231×(2.5873−V) for aconstant current of 5 mA flowing through LED junction 40. Thecalibration factor C must be adjusted when a different constant biascurrent is used.

Whereas silicon diodes with a band gap energy of about 1.1 eV wouldabsorb almost 100% of the light emitted by the LED junctions,gallium-nitride LED junction 40 has a band gap energy of 2.7-2.8 eV andabsorbs only a fraction of 1% of the light that strikes it within ICM10. The low light absorption of gallium-nitride junction compared tosilicon allows junction 40 to be used to sense temperature within chip13 without decreasing the lumen output of ICM 10. Because a silicondiode would absorb almost 100% of the generated light that strikes it,such a diode would have to be covered by a reflective material toprevent absorption. Sapphire substrate 21, however, is substantiallytransparent to white light. Placing a gallium-nitride LED junction underthe flip-chip oriented sapphire substrate 21 and using the junction tosense temperature will not create a dark spot on monolithic LED chip 13.

The gallium-nitride LED junctions of monolithic LED chip 13 emit bluelight with a wavelength of about 452 nanometers when a sufficient drivecurrent is passed through the junctions. The array of sixteen LEDjunctions is covered by a transparent carrier material 41, such as alayer of silicone or epoxy. Particles of phosphor are suspended intransparent carrier material 41. The phosphor converts a portion of theblue light generated by the LED junctions into light in the yellowregion of the optical spectrum. The combination of the blue and yellowlight is perceived as “white” light by a human observer. A thick slurryof phosphor suspended in silicone is dispensed over each of the LEDjunctions. In one embodiment, different types of phosphor particles aredisposed laterally above different LED junctions. Carrier material 41containing various combinations of phosphor particles is dispensed froma micro-pipette above each LED junction. For example, a first type ofphosphor particles is disposed laterally above first string of LEDjunctions 38, and a second type of phosphor particles is disposedlaterally above second string of LED junctions 39.

One of the electronic components embedded in plastic encapsulant 11 is acolor sensor 42, which is shown in FIG. 1 on a slanted portion of uppersurface 16 of ICM 10. The color temperature of the “white” light emittedby the LED junctions and from the phosphor particles is determined usingcolor sensor 42 and other control circuitry of ICM 10. The colortemperature of the light emitted by ICM 10 can be changed by supplyingmore LED drive current to a first string of LED junctions and less LEDdrive current to a second string of LED junctions such that more bluelight is converted into longer wavelength light by the type of phosphorparticles above the first string of LED junctions. For example, a firsttype of phosphor particles disposed laterally above first string of LEDjunctions 38 may convert blue light into a longer reddish light, while asecond type of phosphor particles disposed laterally above second stringof LED junctions 39 may convert blue light into a relatively shorteryellowish light. In one embodiment, the first type of phosphor particlesare a mixture of yttrium aluminum garnet (YAG) and a nitride phosphor,and the second type of phosphor is just YAG. At the initial LED drivecurrents flowing through first string 38 and second string 39, thesensed light emitted from the first and second strings 38-41 has a firstcolor temperature. When the LED drive current supplied to the firststring 38 is increased, the light emitted from the first and secondstrings 38-41 has a second color temperature which is more reddishbecause more blue light is being emitted from below the first type ofphosphor particles. In one implementation, color sensor 42 is thedigital color sensor S11012-01CR from Hamamatsu Photonics, which has anRGB monolithic CMOS photo integrated circuit.

ICM 10 further includes a header socket 43 and four header pins 44-47.Pin 44 is a power terminal through which a supply voltage or a supplycurrent is received into ICM 10. Pin 45 is a power terminal throughwhich the current returns and passes out of ICM 10. Pin 45 is a groundterminal with respect to the power terminal 44. Pin 46 is a data signalterminal through which digital signals are communicated into and/or outof ICM 10. Pin 47 is a signal ground for the data signals communicatedon pin 46. The illustrated example of a module with only four headerpins 44-47 is but one example. In other examples, additional header pinsare provided in the header socket 43.

FIG. 4 is a perspective view of the top of ICM 10 from the other side ofthe module opposite header socket 43. FIG. 4 illustrates how compact ICM10 can be made. All of the power and control circuitry can beaccommodated within the molded plastic encapsulant 11 in close proximityto the LED junctions of monolithic LED chip 13. For example, an activeelectronic component that controls the LED drive current supplied to LEDjunction 38 can be mounted onto interconnect structure 12 at a distancefrom monolithic chip 13 that is less than five times the maximumdimension of the combined LED junctions of monolithic chip 13.Monolithic chip 13 is a square that is 1 mm-10 mm on a side. MonolithicLED chip 13 permits a smaller form factor than an LED array that emitsan equivalent amount of light. ICM 10 provides a correspondingly smallbut yet functional LED package that can take advantage of the smallersize of the monolithic LED light source.

FIG. 5 shows an alternative layout of the LED junctions of monolithicLED chip 13. The embodiment of FIG. 5 has seventeen LED junctionsarranged in a four-by-four matrix with an additional central junctionarea defined for sensor LED junction 40. Redistribution layer 31connects four horizontal strings of four LED junctions each. Inaddition, conductor strips 48 couple the P and N electrodes of sensorLED junction 40 to terminals at the periphery of chip 13. Monolithic LEDchip 13 together with its redistribution layer 31 is then flipped overand mounted onto upper surface 14 of interconnect structure 12. Dashedline 49 shows the periphery of the mounted chip 13. Chip pads 36-37 onchip 13 then contact conductive traces 50 on upper surface 14 ofinterconnect structure 12 and electrically couple chip 13 to power andcontrol circuitry on ICM 10. Metallic vias 51 are disposed laterallybeneath monolithic LED chip 13 except beneath sensor LED junction 40.The vias 51 are thermally coupled to a central thermal pad onredistribution layer 31.

FIG. 6 is a perspective view of the bottom of ICM 10. The lower surface52 of interconnect structure 12 forms the bottom surface of ICM 10. FIG.6 shows the plurality of metallic vias 51 that pass through interconnectstructure 12 from upper surface 14 through to lower surface 52. Themetallic vias 51 are disposed laterally beneath monolithic LED chip 13when ICM 10 is oriented upright as shown in FIG. 1. Vias 51 are filledwith solid metal and conduct heat generated by monolithic LED chip 13 toa heat sink (not shown) attached to lower surface 52 of interconnectstructure 12. For example, the vias 51 are made of copper. No electriccurrent flows through the metallic vias 51.

FIG. 7 shows the bottom of ICM 10. The dashed circle 53 identifies thelocation on the other side of interconnect structure 12 of the circularcentral opening 19 in the upper surface 16 of ICM 10. The dashed square54 identifies the location on the other side of interconnect structure12 of monolithic LED chip 13.

FIG. 8 is a cross-sectional view of ICM 10 of FIG. 7 taken alongsectional line A-A′ (shown on a heat sink 55). Bolts 56 and 57 extendthrough holes 17 and 18 and hold the lower surface 52 of interconnectstructure 12 in good thermal contact with the heat sink 55 through alayer of a thermal interface material (TIM) 58. The thermal interfacematerial 58 is deposited laterally only beneath central opening 19 andunder the metallic vias 51. A thermal insulator 59 is deposited on lowersurface 52 of interconnect structure 12 outside the lateral boundary ofcentral opening 19. Before ICM 10 is mounted on heat sink 55, thermalinsulator 59 is deposited as a layer over bottom surface 52 of ICM 10.Thermal insulator 59 impedes heat that is generated by the LED junctionsand that flows through metallic vias 51 and thermal interface material58 and into heat sink 55 from flowing back up through lower surface 52of interconnect structure 12 and into the electronic components. In someembodiments, thermal insulator 59 is a ceramic or fibrous material.Reference numerals 60 and 61 identify electronic components of controlcircuitry mounted on interconnect structure 12. The injection moldedplastic encapsulant 11 encases and encapsulates interconnect structure12 and the electronic components. In the illustrated example, theinterconnect structure 12 is a multi-layer printed circuit board (PCB),such as an FR-4 PCB. PCB 12 includes three metal layers 62-64 and threefiberglass layers 65-67.

The LED junctions of monolithic LED chip 13, such as LED junction 68,are covered by transparent carrier material 41 containing phosphorparticles. In the embodiment of FIG. 8, a different type of phosphorparticles is suspended in the carrier material 41 that is dispensed overLED junction 68 than the phosphor particles in the carrier material 41over the other LED junctions. For example, by driving an LED drivecurrent through LED junction 68, a reddish light emitted by the phosphorparticles above LED junction 68 can be added to the overall mix of bluelight from the other LED junctions and yellow light from the other typeof phosphor particles. When a drive current is not supplied to LEDjunction 68, the average wavelength of the light emitted from ICM 10 isshorter.

FIG. 9 is a cross-sectional view of ICM 10 of FIG. 7 taken alongsectional line B-B′ (shown on heat sink 55). FIG. 9 shows header socket43 and color sensor 42. Light emitted from the LED junctions and fromthe phosphor particles is sensed by color sensor 42, which has an intakeportion in the slanted surface of upper surface 16 of ICM 10. FIG. 9shows a first type of phosphor particles 69 suspended in siliconedisposed laterally above a first LED junction 70 and a second type ofphosphor particles 71 suspended in silicone disposed laterally above asecond LED junction 72. Color sensor 42 senses the color temperature ofthe light emitted from first LED junction 70, the first type of phosphorparticles 69, second LED junction 72 and the second type of phosphorparticles 71. The color temperature of the overall light being emittedfrom ICM 10 can be changed by increasing the LED drive current suppliedto first LED junction 70 such that a greater proportion of the emittedlight has the wavelength generated by the first type of phosphorparticles 69.

FIG. 10 is a cross-sectional view of ICM 10 of FIG. 7 taken alongsectional line C-C′ (shown on heat sink 55). Electronic components ofthe circuit as seen in the cross-section include a communicationintegrated circuit 73, a microcontroller integrated circuit 74, a FETswitch 75 and a temperature interface circuit 76. Each of these activeelectronic components is a packaged device that is in turn overmolded bythe plastic encapsulant 11 of ICM 10.

FIG. 10 also illustrates that all of the power and control circuitry canbe accommodated within the molded plastic encapsulant 11 in closeproximity to monolithic LED chip 13. For example, microcontroller 74 isan active electronic component that controls the LED drive currentsupplied to LED junction 68 and can be mounted onto interconnectstructure 12 at a distance from monolithic chip 13 that is less thanfive times the maximum dimension of monolithic chip 13. The layout ofICM 10 permits the power and control circuitry to be located withinclose proximity to monolithic LED chip 13 without being overheated fromthe heat generated by the LED junctions. The metallic vias 51 and thethermal interface material 58 laterally beneath chip 13 conduct the heatgenerated by the LED junctions into heat sink 55. Thermal insulator 59prevents the heat that flows through the metallic vias 51 and thermalinterface material 58 from flowing back up through lower surface 52 ofinterconnect structure 12 and into the electronic components.

FIG. 11 is a diagram of the control circuitry 77 of ICM 10 in a firstnovel aspect. ICM 10 is illustrated with heat sink 55 and withmonolithic LED chip 13 covered by transparent carrier material 41.Microcontroller 74 monitors the temperature of LED chip 13 using atemperature interface circuit 78. Temperature interface circuit 78includes a constant current source that supplies a constant current 79to the temperature-sensing GaN LED junction 40 via a contact pads 80 and81. The temperature interface circuit 78 also includes a voltageamplifier that amplifies the sensed voltage across contact pads 80 and81 and supplies the resulting amplified voltage signal T 82 tomicrocontroller 74 via conductor 83. In addition, microcontroller 74monitors the voltage V with which the LED junctions are driven. This LEDdrive voltage is the voltage between sets of contact pads 84 and 85. Acurrent and voltage measuring interface circuit 86 measures this voltagevia conductors 87 and 88. In addition, microcontroller 74 monitors theLED drive current 89 flowing through the LED junctions of LED chip 13.This current 89 flows from pin 90, through contact pads 84, through theLED junctions, through contact pads 85, through current sense resistor91, through FET switch 92 and out of ICM 10 via pin 93. The current andvoltage measuring interface circuit 86 detects the LED drive current 89as the voltage dropped across the current sense resistor 91. Thisvoltage is detected across conductors 88 and 94. The voltage and currentmeasuring interface circuit 86 receives the voltage sense and currentsense signals, low pass filters them, amplifies them, and performs levelshifting and scaling to generate a voltage sense signal V 95 and acurrent sense signal I 96. The voltage and current sense signals 95 and96 are supplied to microcontroller 74 via conductors 97 and 98,respectively.

The T signal 82, the V signal 95, and the I signal 96 are converted intodigital values by the analog-to-digital converter (ADC) 99 of themicrocontroller. A main control unit (MCU) 100 of the microcontrollerexecutes a program 101 of processor-executable instructions. The I, Vand T signals, as well as information received from communicationintegrated circuit 73, are used by the MCU 100 to determine how tocontrol FET switch 92. In the present example, the MCU 100 can controlthe FET switch to be nonconductive, thereby turning off all LEDjunctions. The MCU 100 can control the FET switch to be fullyconductive, thereby turning on the strings of LED junctions to abrightness proportional to the current supplied by the AC-DC converteras controlled by a zero-to-ten-volt signal produced by the MCU asdirected by the control program. ICM 10 receives a substantiallyconstant current via pins 90 and 93 from an AC-to-DC power supplycircuit 102 (see FIG. 14). The AC-to-DC power supply circuit 102 has aconstant current output, the magnitude of the constant current beingcontrollable by a zero-to-ten-volt signal received by the AC-to-DC powersupply circuit. The voltage that results across pins 90 and 93 when thisconstant current is being supplied to ICM 10 is about fifty volts.Microcontroller 74 controls the FET switch 92 to be fully on with nearlyzero voltage across it when LED chip 13 is to be illuminated. Toaccomplish control for a desired LED brightness (desired amount ofcurrent flow through the LED junctions), microcontroller 74 sends azero-to-ten-volt dimming control signal 103 back to the AC-to-DC powersupply circuit 102 via conductor 104, and data terminal 105.Microcontroller 74 uses this control signal 103 to increase and todecrease the magnitude of the constant current 89 being output by theAC-to-DC power supply circuit 102. The circuit components 78, 86, 74 and73 are powered from a low DC supply voltage such as three volts DC. Acomponent voltage supply circuit 106 generates this 3-volt supplyvoltage from the fifty volts across pins 90 and 93. The 3-volt supplyvoltage is supplied onto voltage supply conductor 104. Conductor 107 isthe ground reference conductor for the component supply voltage. Becauseonly a small amount of power is required to power the circuitry embeddedin ICM 10, the component voltage supply circuit 106 may be a simplelinear voltage regulator.

FIG. 12 is a system level diagram of a lighting system 110 thatincorporates ICM 10, power supply circuit 102 and internet connectivitycircuitry 111. The LED junctions of ICM 10 can be monitored andcontrolled remotely by communicating across the internet 112.Information can be communicated from the internet 112, across anethernet connection 113, through the internet connectivity circuitry111, from antenna 114 of the internet connectivity circuitry 111 to theantenna 115 of ICM 10 in the form of an RF transmission, throughtransceiver 116 of the communication integrated circuit 73, and to theMCU 100 of microcontroller 74. Information can also be communicated inthe opposite direction from the MCU 100 of microcontroller 74, throughthe transceiver 116 of the communication integrated circuit 73, fromantenna 115 in the form of an RF transmission to antenna 114, throughthe internet connectivity circuitry 111, across ethernet connection 113,to the internet 112. The lighting system 110 is typically part of aluminaire (light fixture) that is powered by ordinary 110 VAC wallpower. Symbol 117 represents a source of 110 VAC wall power for theluminaire.

FIG. 13 is a diagram of ICM 120 in accordance with a second novelaspect. ICM 120 is similar to ICM 10 of FIG. 11 explained above, exceptthat: 1) ICM 120 of FIG. 13 does not output a 0-10 volt dimming controlsignal, and 2) ICM 120 includes a switching DC-to-DC converter 121. Inthe example of FIG. 13, the switching DC-to-DC converter is a buckconverter. In another embodiment, there is a separate buck converter foreach string of LED junctions on monolithic LED chip 13.

FIG. 14 is a diagram illustrating a first way to drive multiple stringsof LED junctions with multiple buck converters, where the multiple buckconverters are parts of ICM 10. In the example of FIG. 14, the buckconverter block 121 of FIG. 13 actually includes multiple buckconverters 122-125. Each of the strings 126-129 is driven independentlyby buck converters 122-125, respectively. Microcontroller 74 controlseach of the buck converters separately by sending each buck converterdifferent digital control information across different control lines.Microcontroller 74 controls the frequency and/or duty cycle output byeach buck converter's programmable oscillator separately.Microcontroller 74 monitors current flow through each string of LEDjunctions one at a time using the same single current sense resistor 91.Providing multiple buck converters in this way reduces the physical sizeof the inductors of the buck converters. Where four strings of LEDjunctions are separately driven, each by a separate buck converter, theapproximate physical size of the inductor of each buck converter is 2.5mm by 2.5 mm by 1.0 mm. This small inductor size facilitatesencapsulation in a slim ICM profile.

FIG. 15 is a diagram illustrating a second way to drive multiple stringsof LED junctions with multiple buck converters, where the multiple buckconverters are parts of ICM 10. In this case, each string of LEDs has acorresponding dedicated current sense resistor and FET switch. In theexample of FIG. 15, the current sense resistor 91 of FIG. 13 actuallyincludes multiple current sensors 130-133, and FET switch 92 of FIG. 13actually includes multiple switches 134-137. Current sense resistor 130and FET switch 134 are for the first string of LED junctions 126.Current sense resistor 131 and FET switch 135 are for the second stringof LED junctions 127. And current sense resistor 133 and FET switch 137are for the last string of LED junctions 129.

FIG. 16 is a diagram of a lighting system 141 that includes multipleinstances of ICM 120 of FIG. 13. Lighting system 141 includes anAC-to-DC power supply 142, multiple integrated control modules 143-145of the type shown in FIG. 13, and internet connectivity circuitry 111.Bidirectional communication between each ICM 120 and the internet 112via internet connectivity circuitry 111 is the same as described abovein connection with FIG. 12. However, unlike the AC-to-DC power supply102 of the embodiment of FIG. 12 that outputs a regulated substantiallyconstant current (the magnitude of which is adjustable), the AC-to-DCpower supply 142 of the embodiment of FIG. 16 outputs a substantiallyconstant voltage that is only roughly regulated. This roughly regulatedvoltage, in the example of FIG. 16, is 50 volts. This roughly regulatedvoltage is supplied in parallel to the many integrated control modules143-145 via conductors 146 and 147 as shown. The control of the amountof LED drive current supplied to the LED junctions of an individualintegrated control module 120 is controlled by the switching powersupply (for example, a buck converter) within each ICM itself. Each ofthe ICMs 143-145 controls the amount of LED drive current being suppliedto its own LED junctions. The AC-to-DC power supply 142 therefore canoutput a supply voltage that is only roughly regulated. The AC-to-DCpower supply 142 need not receive any 0-10 volt control signal tocontrol its output.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A method comprising: sensing light emitted from afirst LED junction and a second LED junction that are both formed from asingle LED junction and that are included in a monolithic LED chip,wherein a first type of phosphor particles is disposed laterally abovethe first LED junction, wherein a second type of phosphor particles isdisposed laterally above the second LED junction, wherein the first typeof phosphor particles and the second type of phosphor particles aresuspended in a layer of silicone that covers the monolithic LED chip;and increasing an LED drive current supplied to the first LED junctionin response to the sensing of the light emitted from the first LEDjunction, the second LED junction, the first type of phosphor particlesand the second type of phosphor particles.
 2. The method of claim 1,wherein the sensed light emitted from the first LED junction, the secondLED junction, the first type of phosphor particles and the second typeof phosphor particles has a first color temperature, and wherein thelight emitted from the first LED junction, the second LED junction, thefirst type of phosphor particles and the second type of phosphorparticles has a second color temperature when the LED drive currentsupplied to the first LED junction is increased.
 3. The method of claim1, wherein the monolithic LED chip is flip-chip mounted onto aninterconnect structure, wherein an active electronic component controlsthe LED drive current supplied to the first LED junction, wherein themonolithic chip has a maximum dimension, and wherein the activeelectronic component is mounted onto the interconnect structure at adistance from the monolithic chip that is less than ten times themaximum dimension.
 4. The method of claim 3, wherein a front side of themonolithic LED chip is mounted onto the interconnect structure, whereina back side of the monolithic LED chip is disposed opposite the frontside, and wherein the back side is covered by the layer of silicone. 5.The method of claim 3, wherein the monolithic LED chip is flip-chipmounted onto an upper surface of the interconnect structure, wherein ametallic via passes through the interconnect structure from the uppersurface to a lower surface of the interconnect structure, wherein themetallic via is disposed laterally beneath the monolithic LED chip, andwherein no electric current flows through the metallic via.
 6. Themethod of claim 3, wherein the active electronic component is amicrocontroller.
 7. The method of claim 1, wherein no LED junction ofthe monolithic LED chip is coupled to any other LED junction using awire bond.
 8. The method of claim 1, wherein the increasing the LEDdrive current supplied to the first LED junction supplies more LED drivecurrent to the first LED junction than to the second LED junction. 9.The method of claim 1, wherein the first LED junction is part of a firststring of serially connected LED junctions that all share at least onecommon crystalline layer.
 10. The method of claim 1, wherein the firstLED junction is part of a first string of serially connected LEDjunctions that all share a common sapphire substrate, and wherein thelight emitted from the first LED junction exits through the sapphiresubstrate.
 11. A method comprising: sensing a first color temperature oflight emitted from a monolithic LED chip, wherein a first LED junctionand a second LED junction of the monolithic LED chip share at least onecommon crystalline layer, wherein a first type of phosphor particles isdisposed laterally above the first LED junction, wherein a second typeof phosphor particles is disposed laterally above the second LEDjunction, and wherein the first type of phosphor particles and thesecond type of phosphor particles are suspended in a layer of siliconethat covers the monolithic LED chip; and increasing an LED drive currentsupplied to the first LED junction in response to the sensing of thefirst color temperature.
 12. The method of claim 11, wherein the firsttype of phosphor particles convert blue light emitted by the first LEDjunction into relatively longer wavelength reddish light, and whereinthe second type of phosphor particles convert blue light emitted by thesecond LED junction into relatively shorter wavelength yellowish light.13. The method of claim 11, further comprising: sensing a second colortemperature of the light emitted from the monolithic LED chip when theLED drive current supplied to the first LED junction is increased. 14.The method of claim 11, wherein the monolithic LED chip is flip-chipmounted onto an interconnect structure, wherein an active electroniccomponent controls the LED drive current supplied to the first LEDjunction, wherein the monolithic chip has a maximum dimension, andwherein the active electronic component is mounted onto the interconnectstructure at a distance from the monolithic chip that is less than tentimes the maximum dimension.
 15. The method of claim 14, wherein themonolithic LED chip is flip-chip mounted onto an upper surface of theinterconnect structure, wherein a metallic via passes through theinterconnect structure from the upper surface to a lower surface of theinterconnect structure, wherein the metallic via is disposed laterallybeneath the monolithic LED chip, and wherein no electric current flowsthrough the metallic via.
 16. The method of claim 14, wherein the activeelectronic component is a microcontroller.
 17. The method of claim 11,wherein no LED junction of the monolithic LED chip is coupled to anyother LED junction using a wire bond.
 18. The method of claim 11,wherein the first LED junction is part of a first string of seriallyconnected LED junctions that all share a common sapphire substrate, andwherein the light emitted from the monolithic LED chip exits through thesapphire substrate.
 19. The method of claim 11, wherein the first LEDjunction is part of a first string of serially connected LED junctionsthat all share at least one common crystalline layer.
 20. The method ofclaim 11, wherein the first LED junction is part of a first string ofserially connected LED junctions, wherein the second LED junction ispart of a second string of serially connected LED junctions, wherein theLED drive current is supplied to the first LED junction using a firstbuck converter, and wherein a second LED drive current is supplied tothe second LED junction using a second buck converter.